The present invention relates to a color image-forming process, and more particularly, to a process which employs a photosensitive encapsulate and a color precursor to form color images by an exposure-controlled pattern-wise reaction between the color precursor and a developer material.
Imaging systems based on photosensitive encapsulates are known. Berman, U.S. Pat. No. 3,219,446 discloses a transfer imaging process in which an azo blue - black dye is encapsulated with a cross-linkable polymer or a polymerizable monomer as a fluid-droplet containing film or a fluid droplet containing microcapsules. As described, the Berman imaging system is a transfer system which relies upon selectively transferring the encapsulated dye to a copy sheet in correspondence with the image. Imaging is accomplished by image-wise exposing a layer of the encapsulate to electromagnetic radiation to cross-link the polymer, causing the liquid in the exposed capsules to assume a rigid condition and not transfer to a copy sheet. Dye transfer is limited to the unexposed areas of the encapsulate-containing layer.
Phillips, U.S. Pat. No. 3,700,439 discloses a photocopy process wherein Michler's ketone is encapsulated in a conventional manner and provided as a layer on a support. Michler's ketone itself is not a color former, but patterned irradition of the ketone containing capsules produces a latent image of colorless, acid-colorable, dye precursor from the ketone such that upon contact with an acid developer such as acid clay a visible image is obtained. Phillips discloses both a system wherein the exposed imaging sheet is calendered face-to-face with an acid-coated receiving sheet to form images and a system wherein the acid developer is on the same surface as the capsule coating so that after rupturing the capsules on the imaging sheet there is development without transfer.
Berman et al, U.S. Pat. No. 3,072,481 discloses another type of encapsulated light sensitive element which utilizes a light-sensitive material which is readily converted to a colored form when carried in a liquid vehicle but which is insensitive to light when solid. By encapsulating such a material with a volatile solvent, image-wise exposing a layer of the encapsulate and rupturing the capsules to evaporate the solvent, an image is obtained and fixed.
Forris, U.S. Pat. No. 3,001,873, discloses a more complex system wherein the walls of capsules containing a solid dye are photosensitized such that patterned exposure renders the capsules unswellable. By wetting the sheet to swell the unexposed capsules and heating, the dye is immobilized in the unexposed areas. Thereafter, by rupturing the capsules in contact with a receiving sheet there is an image-wise transfer of the dye from the exposed areas only.
Varden, Modern Photography, "What's Ahead?", p. 86 (1958) proposes a system based on gelatin microcapsules where instead of simply gelatin, the capsules are formed from a gelatin silver halide emulsion. According to the author these capsules could contain cyan, magenta and yellow color precursors and be sensitized and used to form color images. The article proposes exposing the sensitized gelatin capsules and hardening them by tanning development (a silver catalyzed process) to prevent the capsules from releasing their contents in the areas of exposure whereby there is a differential release of the capsule contents according to the exposure. There is no evidence in the article indicating that such a system was ever successfully reduced to practice but the fact that the system depends on photographic silver in the capsule wall and would require a wet development step to harden the capsule walls makes it unattractive for many applications.